A valve opening-closing timing control apparatus controls a rotational phase of a driven-side rotational member relative to a driving-side rotational member by supplying and discharging a pressurized fluid to and from an advanced angle chamber and a retarded angle chamber. Furthermore, a lock control portion of the valve opening-closing timing control apparatus switches a state of the lock mechanism, which is a mechanism that locks the rotational phase of the driven-side rotational member relative to the driving-side rotational member, between a locked state and an unlocked state by supplying and discharging a pressurized fluid to and from a lock recess. In JP2004-257313A, hereinafter referred to as Reference 1, a valve opening-closing timing control apparatus that changes a rotational phase of a driven-side rotational member relative to a driving-side rotational member in an advanced angle direction or in a retarded angle direction is disclosed. Note that, the advanced angle direction refers to a direction in which volume of an advanced angle chamber increases and the retarded angle direction refers to a direction in which volume of a retarded angle chamber increases. In a state where the lock mechanism of the valve opening-closing timing control apparatus in Reference 1 is in a locked state, which is a state in which a lock member is inserted into a lock recess so that the lock member and the lock recess are engaged, the valve opening-closing timing control apparatus in Reference 1 supplies a pressurized fluid to a lock recess via a lock controlling supply passage. Accordingly, the lock mechanism is switched to an unlocked state, which is a state in which the lock member is retracted from the lock recess. Simultaneously, the pressurized fluid is supplied to the advanced chamber or the retarded angle chamber via a phase controlling supply passage so that the rotational phase is changed in the advanced angle direction or in the retarded angle direction.
In the valve opening-closing timing control apparatus of Reference 1, in a state where the pressurized fluid is supplied by a fluid pump driven by an internal combustion engine, the pressurized fluid having an appropriate flow rate, or pressure, is not discharged from the fluid pump at a time at which an engine is started. Accordingly, in JPH11-13429A, hereinafter referred to as Reference 2, a valve opening-closing timing control apparatus using a pressurized fluid stored in an accumulator is disclosed. The valve opening-closing timing control apparatus disclosed in Reference 2 may retain an appropriate fluid pressure even at the time at which the engine is started. The valve opening-closing timing control apparatus disclosed in Reference 2 supplies the pressurized fluid stored in the accumulator to an advanced angle chamber or a retarded angle chamber in order to stabilize an operation of a phase control portion to control a rotational phase at the time at which the engine is started.
Furthermore, the rotational phase of the driven-side rotational member relative to the driving-side rotational member becomes most advanced angle phase when a partition portion partitioning a fluid pressure chamber into the advanced angle chamber and the retarded angle chamber moves to a position at which volume of the advanced angle chamber becomes maximum. The rotational phase becomes most retarded angle phase when the partition portion moves to a position at which volume of the retarded angle chamber becomes maximum. In JP2010-84756A, hereinafter referred to as Reference 3, a valve opening-closing timing control apparatus for controlling opening-closing timing of an exhaust valve is disclosed. The valve opening-closing timing control apparatus disclosed in Reference 3 includes a most advanced angle lock mechanism that locks a rotational phase at the most advanced angle phase. The most advanced angle lock mechanism includes a lock member and a lock recess. The lock member is inserted into the lock recess to engage with the lock recess and is retracted from the lock recess to disengage with the lock recess. The lock member and the lock recess are configured to engage and disengage with each other only at a time at which the rotational phase is at the most advanced angle phase. Accordingly, at a time before the rotational phase reaches the most advanced angle phase, which in other words is at a time before the lock member enters the lock recess, a relative rotation between a driving-side rotation member and a driven-side rotation member is not restrained.
In the valve opening-closing timing control apparatus disclosed in Reference 1, the pressurized fluid for lock release and the pressurized fluid for phase change are simultaneously supplied. Accordingly, when the rotational phase of the driven-side rotational member relative to the driving-side rotational member is attempted to shift while each of the advanced angle chamber and the retarded angle chamber is in a state where the pressurized fluid is discharged and while the lock mechanism is retained in the unlocked state by supplying the pressurized fluid for lock release to the lock recess, the fluid pressure of the pressurized fluid for lock release may fall during a period during which the pressurized fluid for phase change is supplied to either the advanced angle chamber or to the retarded angle chamber to shift the rotational phase until the fluid pressure of the pressurized fluid supplied to either the advanced angle chamber or to the retarded angle chamber rises to a predetermined pressure. In a state where the fluid pressure of the pressurized fluid for lock release has fallen, the lock member that is retracted from the lock recess may engage again with the lock recess. In a state where the lock member is engaged again with the lock recess, the rotational phase may not be smoothly changed.
The valve opening-closing timing control apparatus disclosed in Reference 2 requires equipment of an accumulator that may store large volume of a pressurized fluid corresponding to maximum volume of the advanced angle chamber and the retarded angle chamber in order to supply the pressurized fluid stored in the accumulator to the advanced angle chamber or to the retarded angle chamber. In a case where the pressurized fluid stored in the accumulator is supplied to the lock recess in addition to the advanced angle chamber or the retarded angle chamber, the accumulator is required to contain a larger volume of the pressurized fluid. In general, such accumulator is installed as a unit on an engine body at a position close to the valve opening-closing timing control apparatus. As an alternative, the accumulator may be integrated into an engine cover in advance. As a result, an engine becomes large in size and an arrangement adjustment between other auxiliary units in an engine room may become complicated, which are considered as drawbacks.
Furthermore, in a valve opening-closing timing control apparatus equipped with an intermediate lock mechanism, when a phase is changed from an intermediate lock phase to most retarded angle phase by using the pressurized fluid stored in the accumulator, sufficient amount of the pressurized fluid may not be supplied to the intermediate lock mechanism as a result of rapid volume change in the retarded angle chamber. Without sufficient hydraulic pressure required for lock release, an unlock process may not be smooth, which is considered as a problem.
In addition, in the valve opening-closing timing control apparatus disclosed in Reference 3, the rotational phase of the driven-side rotational member relative to the driving-side rotational member may not be swiftly locked at most advanced angle phase. More specifically, on the driven-side rotational member that integrally rotates with a camshaft for opening and closing the exhaust valve, for example, an anti-torque of cams is exerted via the camshaft. In a state where the anti-torque is exerted on the driven-side rotational member such that the driven-side rotational member rotates relative to the driving-side rotational member in a direction opposite to the most advanced angle phase, a fluttering may occur at a moment at which the driven-side rotational member reaches a most advanced angle phase position. The fluttering is a rotation of the driven-side rotational member in the direction opposite to the most advanced angle phase caused by a cam torque exerted on the driven-side rotational member. When the fluttering occurs, even at a time at which the driven-side rotational member reaches the most advanced angle phase position, the lock member may lose a timing to be inserted into the lock recess. Accordingly, the lock member may not be swiftly locked at the most advanced angle phase. Such fluttering may similarly occur in a valve opening-closing timing control apparatus equipped with a most retarded angle lock mechanism including a lock member and a lock recess, the lock member and the lock recess that engage with each other when the lock member is inserted into the lock recess and disengage with each other when the lock member is retracted from the lock recess only at a time at which the rotational phase is at the most retarded angle phase.
A need thus exists for a valve opening-closing timing control apparatus, which is not susceptible to the drawbacks mentioned above.